Common Knowledge
by Starkreactor
Summary: John can't sleep because his infant daughter can't sleep. Sherlock can't think because of all the crying. And Mary can't seem to calm the infant either. Sherlock's robotic response to the problem reveals something very human at his core. Fluffy one shot!


So, I was thinking about Sherlock and how he would react around a baby and the whole comment about his not having a heart and this popped up. For the record, in my little world here, John and Mary are married and have an infant named Clara.

Enjoy!

* * *

><p>John Watson groaned and rolled over, burying his head under his pillow. Clara was crying again.<p>

"I'll get her." Mary said sleepily, getting out of their bed and trudging down the hall for the fourth time that night. John sighed in relief, closing his eyes against his splitting headache and trying not to think about how he had to get up for a 48 hour shift in three hours. The infant's wails continued for a few minutes before quieting. John was barely conscious when his wife returned to their bed.

A half-hour later, and the baby was crying again. John started awake, groaning and scrubbing his fingers into his eyes. He was going to be beyond fried when he got to work in the morning. Wasn't this part of what he was hoping to get away from when he moved out of 221b?

"I'll get her." Mary said again, obviously very groggy.

"No," John said. "I've got her. I can't sleep anyway."

Moving down the hall wearily, John scooped up his and Mary's tiny baby, cradling and rocking her in an effort to quiet her.

"You know, it would be much easier to think if it was a bit quieter." a deep voice commented from his spot in the doorway. Watson fought the urge to put his child down and strangle the insufferable detective behind him.

"And I could be getting a decent night's sleep, but it looks like that's not going to happen either." He said testily, still bouncing the crying baby gently.

"I only agreed to stay with you because I needed a place for cheap while they are re-building 221b from the recent incident. You promised me I'd still be able to work." Sherlock said icily.

John rounded on the detective. "I _let_ you stay here because you half burned down _your_ flat with another insane bloody _experiment_." He said, teeth grit in agitation and fighting not to yell for Clara and Mary's sakes. "If you can't think properly because of my baby in my flat, then you can just leave."

"Impossible. It's raining quite heavily outside and the rain would be an even greater nuisance than your offspring." Holmes answered bluntly.

Watson's blood boiled. "Get. Out."

To his surprise, the other man actually retreated.

It took another fifteen minutes before Clara calmed and fell back to sleep.

It took another ten before John was jolted out of his much needed rest by more crying. Fighting the urge to scream and cry and pass out all in the same instant, John lay on his back, trying to muster the courage to get up again. Just when he was about to get up, the crying quieted and stopped altogether. John's eyes closed in momentary relief, but then the knowledge that Clara had never just stopped on her own before and his ex flat mate was probably still in the house made him get up in a panic. He ran to Clara's room, only to be greeted by the strangest sight.

Sherlock was laying on the couch in the baby's room, with Clara curled on his chest. The infant had her fist tucked up by her face, her head turned towards John and her feet tucked under her. Sherlock was rubbing soothing circles in the baby's back, and her eyes were closed in sleep.  
>John gaped. At first he was shocked, but then his lack of sleep gave way to unreasonable anger. "How on bloody earth did you get her to quiet down?"<p>

Sherlock turned his head to face John, his silvery eyes lazily looking up at the irate parent. "Really John, as a doctor I thought it would be a simple deduction." He said, loud enough for John to hear but not loud enough to wake Clara.

"You- she's listening to your heartbeat." John suddenly realized.

"Very good." Sherlock drawled sarcastically. "You of all people should know that an infant with insomnia not caused by the need for food or a change will fall asleep fastest to the sound of a human heartbeat. Simple instinct bred from the womb."

"But...but..." John spluttered. "I've tried that! She doesn't respond."

Sherlock scoffed. "I should think not. The rasping in your lungs caused by an oncoming bout of the flu would certainly dampen the effect."

"How did you..." Watson began, before stopping and breathing in deeply. His breath hitched some and he could feel a slight rattle in his chest.

"Not to mention an infant will respond better to a calm heartbeat than an agitated one. All in all, you were not an adequate sleep aid for Clara."

John felt his anger flare. "So my heartbeat isn't good enough now?" He demanded. "Is that what you're telling me?"

Sherlock merely looked back up at the ceiling, Clara still fast asleep to the sound of his heartbeat. "Get some sleep John. Oh, and I'd call off if I were you. It would be a shame to give your thyroid patient an infection."

John pursed his lips. He was sick of Sherlock knowing everything about his life, but honestly, what was he going to do about it? "Why did you do it?" he asked suddenly. "You don't like to be touched, and you were never interested in Clara before. You didn't even want to hold her when she was first born."

"I had a problem. I couldn't think with her crying. I solved the problem. Now I can get back to my case, you can go back to sleeping, and Clara will be more tolerable in the morning because if it. I don't see what the problem is. I'm doing us all a favor."

"By having a heartbeat." John muttered. "Just, be gentle with her." He said finally, turning from the room.

Honestly, the warning seemed foolish. As eccentric as Sherlock was, there was no doubt that he would be nothing if not tender with the infant curled trustingly over his beating heart.

When John woke up two and a half hours later, his alarm blaring gratingly in his ear, he got up wearily for work. Finally ready, he went to Clara's room to check on her, only to find that she and Sherlock hadn't moved. Clara was still asleep, but much to John's surprise, so was Sherlock. The detective still lay on his back, one arm curled protectively around Clara, the other one resting on her back. John might have thought he was resting, except for the fact that Sherlock's breaths were much too deep and slow for someone awake. He paused for a moment, the extra sleep having melted away most of the irrational anger he'd had just a few hours ago.

Closing the door gently, he knew his daughter would be safe.

Because despite what many people had bitingly tried to prove, Sherlock Holmes definitely had a heart.


End file.
